For use with concrete and other forms of masonry, a wide variety of anchors and fasteners have been developed. These anchors and fasteners may be installed manually or by use of a power tool. In recent years, a self-tapping concrete fastener has been developed and marketed. This fastener has external threads and is driven into a hole previously drilled in the concrete. The hole may be drilled by a masonry drill bit chucked in a power tool and driven at a relatively high rpm. 2. Description of the Prior Art
If the same power tool is used for both the drilling and fastener driving operations, the masonry drill bit must be removed from the power tool or otherwise deactivated, and the fastener coupled to the power tool by means of a suitable adapter. If many fasteners are to be used, any repeated removal and/or re-insertion of an adapter into the power tool is inconvenient, time consuming and hence costly.
Another arrangement is disclosed in U.S. Pat. No. 3,965,510. There, a driving mandrel carrying a masonry drill bit is telescopically received within the body portion of a combination attachment for a conventional electric drill. The body may be alternately retracted and advanced relative to the mandrel. In the retracted position of the body, the mandrel and hence the drill bit are exposed for drilling the required hole. In the advanced position of the body, the drill bit (which is being continuously rotated) is enclosed by the body. The end of the body carries an adapter insert having a socket therein for receiving the head of the masonry fastener.
While the structure disclosed in this '510 patent facilitates rapid drilling in concrete and subsequent installation of the threaded masonry fasteners, nevertheless, the power tool is driven at a substantially constant speed for both the drilling and fastener driving operations. This is undesirable. Ideally, the fastener driving operation should be performed at a substantially lower rpm than the drilling operation; otherwise, the threads may become stripped and the fastener may not be anchored securely. If the power tool is a two-speed drill with a mechanical shifter, this disadvantage may be somewhat alleviated. However, the different speeds are usually selected for drilling purposes, not drilling and fastener driving purposes, and the lower speed is still not ideally suited for the subsequent fastener driving operation. Furthermore, the addition of speed selectors and associated mechanisms results in a more expensive power tool; and besides, the speed-changing operations are time consuming.
Moreover, if the power tool is provided with a well-known trigger-operated electronic circuit providing a substantially unlimited speed range, it will be difficult for the operator to maintain the selected lower speed during the fastener driving operation. Besides, the output torque falls off substantially at the lower speeds, and this is quite undesirable for a masonry fastener driving operation.
Additionally, power tools have been disclosed in which multiple driving spindles protrude from the tool housing for alternately driving various tool elements at different speeds. One example is the power tool disclosed in U.S. Pat. No. 1,216,047. However, these disclosures still require removal of the drill bit or other tool element; otherwise, the exposed drill bit, which is continually driven, would constitute a safety hazard. Thus, these disclosures appear to be impractical for a multi-purpose tool for repeated concrete drilling and fastener driving operations.
The prior art has also disclosed other combination tools, such as the combination drill and screwdriving tool of U.S. Pat. No. 3,932,904. In this '904 patent, an axially-displaceable sleeve may be retracted rearwardly and held in a stationary position while the drill bit is exposed for drilling a hole. After the hole is drilled, the sleeve may be advanced forwardly to enclose the drill bit. The sleeve is then locked to the driving spindle for driving a screw or other fastener into the drilled hole at the same speed. In this disclosure, the sleeve is always mounted on the core body and retained against complete removal therefrom. This configuration is not only impractical for deep hole drilling but is only suited to drive hex head fasteners, wherein the deep socket drive will allow the drill bit to pass through the drive socket when the driving sleeve is retracted. Fasteners having cross-slotted or slotted heads cannot be used in this system.
Thus, it will be appreciated that despite the numerous patents and commercial devices which are available, a totally practical solution to the problem has not been forthcoming.